Vacuum drying



J. M. BAER VACUUM DRYING Dec. 28, 1948.

Filed Feb. 28, 1944 Patented D ec. 28, 1948 l UNITED STATES PATENToFFlcE VACUUM DRYING John M. Baer, Chicago, Ill., assigner, by meme K assignments, to Guardite Corporation, Wilmington, Del., a corporation of Delaware Application February 288. 1944, Serial No.1 524,177

's claim. (c1. 34-3'1) v 1 This invention relates to a process of vacuum drying and more particularly to the drying of water-containing materials at low pressure under radiant heat in an atmosphere oi superheated steam. v

The invention may be carried out in apparatus of v arious types but reference is made to details of a preferred apparatus in Heineman application, Serial No. 520,773, filed February 2, 1944 now Pat. No. 2,437,552, issued March 9, 1948.

The invention is illustrated diagrammatically in the drawings'in which the ligure represents a vacuum chamber i provided with a vacuum line ii leading to suitable evacuating apparatus. The chamber is provided with an' entrance door i2 and an exit door iand is divided into a cooking chamber Il and a drying chamber i5. Suitable conveying apparatus i3 arranged in tiers is provided to carry the material through the Ydrying chamber, and heating coils il are arranged in a series of banks through the chamber. Means Is is provided for introducing super heated steam to the entrance end of the drying chamber i5, and a second entrance for superl heated steam I9 is provided at the exhaust end. A lock chamber is provided at the exhaust end and this is equipped with separate evacuating means 2i and a door 22. Details of a lock chamber are described in Heineman application, Serial No. 501,399, filed September 3, 1943 now Pat. No. 2,373,891 issued April 17, 1945; details of a radiation system are described in Heineman application 500,949, led September l, 1943 now abandoned; and details of a suitable entrance door i2 are described in Heineman application Serial No. 501,398, illed September 6, 1943 now Pat. No. 2,370,660, issued March 6, 1943.

The cooking chamber iii is also provided with an evacuation port 25 and an inlet 26 for superheated steam. Details oi' a conveying system ning the material undergoing drying is subjected to superheated steam from the line iland this steam moves concurrently with the material undergoing drying until it reaches substantially the middle point in the chamber from where it is removed through the line il. During the course oi' this motion, the initially superheated steam is increased in volume by moisture evaporated from the product undergoing drying so that the velocity of its movement is increased but its temperature is not. In actual practice the steam is permitted to drop somewhat in temperature upon contact with the ilrst material and then is maintained at substantially constant temperature until it reaches the middle of the chamber. From that point on the temperature cycle may be held constant or may be reversed. This flexibility of operation is made possible by the introduction of the second'steam stream from the line i9. The result is that the material be dried, during the latter half of its progress through the drying chamber, passes countercurrently to the superheated steam which it encounters in decreasing amounts.

The cooking chamber id is used to precook or to blanch the material to be dried. In that chamber the material is subjected to a high ,vacuum under conditions adapted to remove substantially all air and produce an atmosphere substantially of steam, and it is then rapidly heated by the introduction oi. superheated steam to a relatively high temperature and pressure and is held there for a short period, after which the pressure is again reduced with consequent and immediate lowering of temperature.

`tray and one above'the top tray. Temperature recordings were taken between the third and fourth trays unless otherwise indicated. The material was spread upon the trays in layers about V2 inch deep and generally at about 11/2 lbs. per square foot.

As an example of the process, ordinary pork meat was cut into small pieces, generally less than V2 inch in any dimension and cooked in open kettles. The temperature was brought to about F. in one-half hour and maintained at that temperature for approximately 3A hour. During this procedure it lost a considerable portion oi' its weight. It was loaded on trays having screen bottoms, the loading being at the rate of approximately one pound per square foot. The material was supplied to the cookingfchamber,

air removed, and the material cooked for one-- half minute at 20 inches vacuum and a temperature approximately 160 to 165 F. The material was then supplied to the drying chamber wherein an absolute pressure of approximately 63 mm. was maintained. 6300 lbs. of pork was supplied to the apparatus and 2974 lbs. removed, the balance representing Water loss. Steam pressure of 110 lbs. was maintained in steam banks I and 2; 90 lbs. in banks 3 and 4;,50 lbs. in bank 5; 30 lbs. in banks 6 and 1; and 10-1bs. in banks 8 and 9. The observed temperature immediately above the fourth tray from the top (third tier from the bottom) at the start of the drying operation, was 313 F. in banks I and 2; 327 F. in banks 3 and A; 299 F. in bank 5; 281 F. in banks; 271 F. in bank 1; 268 F. in bank a; and 253 F. in bank 9.

When the operation was under way, these temperatures had dropped to 234 F'. in banks I' and 2; 265 F. in banks 3 and s; 244 F. in bank 5; 232r. in bank s; 235 F. in bank 1; 229 F. in

bank 8; and 212 F. in bank 9.v The temperature of the meat was of course markedly lower than these temperatures.

The pressure varied in the chamber, normally being about 21/2 inches absolute, but ranging upwardly to as much as 5 inches on occasions when the cooking chamber and outlet entrance were opened.

The moisture content of the product going into the cooker averaged approximately 53%. In the cooker the moisture content remained about constant, although some samples showed an increase. The nal moisture content was approximately 3.6% with a fat content of 40.9%. The drying cycle employed was 90 minutes. The material showed an average reconstitution with water of about '78%, this figure being based upon the rehydration ratio divided by the dehydration ratio. 'Ihe rehydration ratio is the rehydrated weight over the dehydrated Weight. The dehydration ratio is the raw weight over the dehydrated weight. The reconstitution coefficient is, therefore, the rehydrated weight over the raw weight. which is the same as the rehydration ratio over the dehydration ratio.

During the operation superheated steam was introduced through the line I8 at the entrance to the drying chamber, and through the line I9 near the exhaust end thereof. This steam may be superheated in any desirable fashion. As a minimum amount of superheat the steam may be expanded from the line pressure of approximately 100 lbs. through a 1inch pipe to the/vacuum. It will be observed that the relative humidity of the steam flowing concurrently with the material increases in th'edirection of movement of the material while the relative humidity of the steam flowing counter-currently to the material decreases in the direction of movement of the material.

The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom.

What I claim as new, and desire to secure by Letters Patent, is:

1. 'I'he method of drying a moisture-containing product which comprises substantially removing air therefrom and replacing it with an atmosphere of steam at low absolute pressure, introducing the deaerled product in successive increments under vacuum to a drying zone, supplying an atmosphere substantially of superheated steam, moving the product in incrementsthrough the zone in a predetermined course concurrently with a surrounding stream of said superheated steam in contact therewith while subjecting the product to intense radiant energyon-all sides from a source adjacent the product other than the superheated steam in contact therewith, then moving the product countercurrent to another stream of superheated steam introduced into the drying zone from an outside source to complete the drying, simultaneously introducing succeeding increments of the product concurrently with succeeding portions of the first stream of steam, and-removing both currents of steam together centrally of the drying zone.

2. The method as set forth in claim 1, in which the` temperatures of the respective currents of steam are initially substantially diierent.

3. The method as set forth in claim 1, in which the temperature of the concurrent stream current progressively drops while its moisture content increases.

4. The method as set forth in claim 1, in which the temperature of the countercurrent steam current` progressively rises in the direction of its movement.

5. The method of drying a moisture-containing product which comprises substantially removing air therefrom, introducing the product in successive increments to a drying zone having an atmosphere substantially of superheated steam under vacuum supplied from an exterior source, moving tihe product in increments through a drying zone in a predetermined course concurrently with a surrounding stream of said superheated steam in contact therewith while subjecting the product to intense radiant energy on all sides from a source closely adjacent the product and other than the atmosphere 'in contact therewith, then moving the product countercurrent'to anothery stream of superheated steam in the drying zone to complete the drying, simultaneously introducing succeeding increments of the product concurrently to the drying zone with succeeding portions of the iirst stream of steam, the product in the iirst stream of steam being subjected to gradually increasing relative humidity, and'subjecting the product in the second stream to progressive decreasing relative humidity.

6. The method of drying a moisture-containing product which comprises treating the product to remove substantially al1 air therefrom and replac ing it with an atmosphere of steam at low absolute pressure, introducing the product into a first dry-- ing zone having an atmosphere substantially of superheated steam, moving the product through said first zone in a predetermined course concurrently with a -stream of superheated steam contacting the product, subjecting the product in said rst zone to intense radiant energy applied from a source closely adjacent-the product, then moving the product through a second drying zone countercurrently to another stream of superheated steam to complete the drying, the source of all said radiant energy being other than the superheated steam contacting the product and said Vsuperheated steam being supplied to the drying zones from outside sources, whereby said product is subjected to gradually increasing relative humidity during its passage through the irst zone and is subjected to gradually decreasing relative humidity during its passage through the second zone.

JOI-IN M. BAER.

(References on following page) REFERENCES CITED The following references ar lfile of this patent:

UNITED STATES PATENTS Number Name Date Fickett May 3, 1881 Nichols Mar. 21, 1882 Prati; July 29, 1902 Lain Aug. 3, 1926 Jungels Jan. 20, 1914 Price Dec. 19, 1916 Hare Apr. 8, 1924 e of record in tle Number 10 Number 

